Taxonomy & naming
The species was described by Carl L. Hubbs in 1936 as Cichlasoma pearsei, in his treatment of the fishes of the Yucatán Peninsula collected during the Carnegie Institution's expeditions; the epithet honours Arthur Sperry Pearse (1877-1956), the American zoologist who led the Yucatán fieldwork. Like its relatives it sat for decades in the omnibus Cichlasoma and was later shuffled through Theraps and Herichthys. The genus Cincelichthys was erected by McMahan & Piller in 2015 for this species and its type-species relative Cincelichthys bocourti, diagnosed by the spatulate, chisel-like, side-to-side flattened oral teeth that set the pair apart from neighbouring heroine genera. The Catalog of Fishes (Fricke, Eschmeyer & Van der Laan) lists the species as Cincelichthys pearsei (Hubbs 1936). The genus belongs to tribe Heroini among the herbivore-leaning Middle American cichlids; as with bocourti, FishBase still flags its exact placement as incertae sedis pending a fuller revision of the heroines.
Morphology
Cincelichthys pearsei is a large, tall, laterally compressed cichlid; FishBase gives a maximum around 8 in standard length, while hobbyist accounts of fully-grown fish report considerably larger total lengths, so this is unmistakably a big cichlid. The body is deep and high-backed with a steep forehead, and the colour is a muted olive-tan to greyish ground, usually with a series of darker vertical bars across the flanks that can be flashed or suppressed, plus dusky markings on the body and dorsal. As in its congener the diagnostic feature is the dentition — spatulate, chisel-edged teeth squared at the tip and flattened side-to-side, set in fleshy lips, built for cropping and rasping plant matter rather than seizing prey. Sexual dimorphism follows the heroine pattern: males grow larger and deeper-headed with longer, more pointed dorsal- and anal-fin filaments and can develop a modest nuchal hump, while females are smaller and rounder-bodied; both sexes intensify their barring and darken when breeding.
Habitat
The species is native to the Atlantic slope of southeastern Mexico and northern Guatemala, broadly distributed through the Grijalva-Usumacinta drainages of Campeche, Tabasco and Chiapas southward into the Petén of Guatemala, in systems such as the Río Tulijá, Río Usumacinta, Río Candelaria and Río Lacanjá. Its element is the pantano — the marsh, lagoon and slow river reach thick with aquatic and bankside vegetation — from which it takes its common name. These are warm, lowland, often turbid waters subject to a strong seasonal flood pulse, fed by limestone-influenced drainages so that the water tends to be hard and alkaline; the species also tolerates brackish conditions in coastal stretches. Reported parameters are warm (around 79–86 °F) with high pH (about 7.5-8.5) and moderate-to-high hardness. It favours the vegetated, sluggish habitats where its plant-cropping habits pay off, rather than fast, open, rocky water.
Feeding
Cincelichthys pearsei is among the most thoroughly herbivorous of the larger Central American cichlids. It is reported feeding directly on aquatic and terrestrial plants — including the vegetation lining the river banks — cropping leaves and stems with its chisel-edged teeth, and grazing algae and aufwuchs from submerged surfaces. Its large gut and modest, plant-adapted dentition mark it as a true browser-grazer, taking the small invertebrates bound up in the vegetation and biofilm as an incidental animal supplement rather than as primary prey. In the dense, weedy pantano habitats it occupies, this plant-based feeding lets it grow large on a resource that few of its neighbours exploit so directly, filling a herbivore's niche in the lowland food web.
Mating
The pantano cichlid is a monogamous, biparental substrate spawner. Pairs form and establish a territory, defending it with the standard heroine repertoire of lateral displays, fin-spreading and jaw contact, and intensifying their colour and barring as breeding nears. Hobbyist accounts describe it as one of the more peaceable large Central Americans outside of breeding, living in pairs or small groups and capable of becoming quite tame, but a spawning pair turns territorial and protective. Courtship involves jointly selecting and cleaning a spawning surface — a flat rock or root — a shared preparatory ritual that signals readiness and binds the pair before eggs are laid.
Breeding
Cincelichthys pearsei is an open substrate spawner with biparental care. The pair cleans a flat rock or submerged root and the female deposits adhesive eggs on it in rows; both parents then tend the clutch, fanning and cleaning the eggs, which hatch in roughly five days in warm water. The wrigglers are moved to pits and, once free-swimming, are guarded as a dense school by both parents and shepherded through the vegetated habitat. In captivity the species spawns readily for a compatible pair given warm, hard water — keepers cite a temperature around 81 °F as ideal for breeding — and the fry take fine foods and newly-hatched brine shrimp as they grow. It is a dependable, attentive parent in the mould of the larger heroines, and an undemanding breeder once paired.
In the aquarium
The pantano cichlid is kept by Central American cichlid enthusiasts and is valued as one of the more even-tempered large heroines — described as relatively peaceful, capable of becoming tame, and a good 'big but manageable' cichlid for the experienced keeper. Because it grows large, it needs a sizeable tank: at least around 98.5 in of length and several hundred litres for an adult or pair, furnished with a sandy bottom, rocks and driftwood for cover and spawning sites. Water should be warm and hard to match its limestone-lowland home — temperature 75–86 °F (around 81 °F for breeding), pH 7.5-8.5, hardness in the moderate-to-high range (roughly 3-14 dGH reported in the hobby) — with strong filtration and regular large water changes to support a big, plant-processing fish. The diet must be plant-forward: spirulina- and vegetable-based foods, blanched greens and algae wafers as the staple, with frozen and live invertebrates (artemia, mosquito larvae) as supplements; a purely meaty diet does not suit its herbivorous gut. Tankmates should be other peaceful-to-moderate cichlids of similar size; it is less aggressive than many guapotes but will still hold and defend a breeding territory, so it is best thought of as a large-cichlid community fish rather than a true peaceful community species.
Conservation
The IUCN Red List assesses Cincelichthys pearsei as Least Concern (assessed 27 November 2018), reflecting a fairly broad distribution across the Grijalva-Usumacinta lowlands from Campeche, Tabasco and Chiapas into the Petén, together with an apparently resilient population and a tolerance for the variable, brackish-tinged conditions of its habitat. It carries no CITES listing. As a regional food fish it is harvested, but not at a level the assessment flags as a population threat. The broader pressures on its habitat are those bearing on the whole Usumacinta-Grijalva basin: large dams and proposed hydroelectric development that alter flow and the flood pulse on which its pantano habitats depend; deforestation, agriculture and pollution in the lowlands; and the spread of introduced fishes, especially African tilapias. The species' wide range, adaptability and unusual herbivorous niche buffer it for now, and its status is secure, but it shares the long-term vulnerabilities of a basin under accelerating human pressure.